I. THE EUKARYOTIC CELL
A. COMPOSITION AND FUNCTIONS OF EUKARYOTIC CELLULAR STRUCTURES
6. The Cytoskeleton
The overall purpose of this Learning Object is to learn the chemical makeup and the functions associated with the cytoskeleton in eukaryotic cells.
LEARNING OBJECTIVES FOR THIS SECTION
The cell is the basic unit of life. Based on the organization of their cellular structures, all living cells can be divided into two groups: prokaryotic and eukaryotic (also spelled procaryotic and eucaryotic). Animals, plants, fungi, protozoans, and algae all possess eukaryotic cell types. Only bacteria have prokaryotic cell types.
Eukaryotic cells are generally much larger and more complex than prokaryotic. Because of their larger size, they require a variety of specialized internal membrane-bound organelles to carry out metabolism, provide energy, and transport chemicals throughout the cell.
We will now look at the cytoskeleton of eukaryotic cells.
The Cytoskeleton (def)
The cytoskeleton is a network of microfilaments, intermediate filaments, and microtubules. The cytoskeleton functions to:
1) give shape to cells lacking a cell wall;
2) allow for cell movement, eg, the crawling movement of white blood cells and amoebas or the contraction of muscle cells;
3) movement of organelles within the cell and endocytosis;
4) cell division, ie, the movement of chromosomes during mitosis and meiosis and the constriction of animal cells during cytokinesis.
We will now take a closer look at microtubules, microfilaments, intermediate filaments, centrioles, flagella, and cilia.
Microtubules are hollow tubes made of subunits of the protein tubulin. They provide structural support for the cell and play a role in cell division, cell movement, and movement of organelles within the cell. Microtubules are components of centrioles, cilia, and flagella (see below).
Microfilaments are solid, rodlike structures composed of actin. They provide structural support, and play a roll in phagocytosis, cell and organelle movement, and cell division.
c. Intermediate filaments
Intermediate filaments are tough fibers made of polypeptides. They help to strengthen the cytoskeleton and stabilize cell shape.
Centrioles are located near the nucleus and appear as cylindrical structures consisting of a ring of nine evenly spaced bundles of three microtubules. Centrioles play a role in the formation of cilia and flagella. During animal cell division, the mitotic spindle forms between centrioles.
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Updated: July 12, 2006
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